Bsi bs en 14620 3 2006

BS EN
14620-3:2006

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Design and
manufacture of site
built, vertical,
cylindrical,
flat-bottomed steel
tanks for the storage of
refrigerated, liquefied
gases with operating
temperatures between
0 °C and p165 °C —
Part 3: Concrete components

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BRITISH STANDARD

The European Standard EN 14620-3:2006 has the status of a

British Standard

ICS 23.020.10

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BS EN 14620-3:2006

National foreword
This British Standard was published by BSI. It is the UK implementation of
EN 14620-3:2006. This standard, together with BS EN 14620-4:2006,
supersedes BS 7777-3:1993 which is withdrawn.

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A list of organizations represented on PVE/15 can be obtained on request to its
secretary.
This publication does not purport to include all the necessary provisions of a
contract. Users are responsible for its correct application.

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Compliance with a British Standard cannot confer immunity from
legal obligations.

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The UK participation in its preparation was entrusted to Technical Committee
PVE/15, Storage tanks for the petroleum industry.

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This British Standard was
published under the authority
of the Standards Policy and
Strategy Committee
on 29 December 2006

© BSI 2006

ISBN 0 580 49777 1

Amendments issued since publication
Amd. No.

Date

Comments


EN 14620-3

EUROPEAN STANDARD
NORME EUROPÉENNE

EUROPÄISCHE NORM

September 2006

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English Version

Design and manufacture of site built, vertical, cylindrical, flatbottomed steel tanks for the storage of refrigerated, liquefied
gases with operating temperatures between 0 °C and -165 °C Part 3: Concrete components

Auslegung und Herstellung standortgefertigter, stehender,
zylindrischer Flachboden-Stahltanks für die Lagerung von
tiefkalt verflüssigten Gasen bei Betriebstemperaturen
zwischen 0 °C und -165 °C - Teil 3: Bauteile aus Beton

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Conception et fabrication de réservoirs en acier à fond plat,
verticaux, cylindriques, construits sur site, destinés au
stockage des gaz réfrigérés, liquéfiés, dont les
températures de service sont comprises entre 0 °C et -165
°C - Partie 3: Constituants béton

This European Standard was approved by CEN on 20 February 2006.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European

Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the Central Secretariat or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,
Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania,
Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.

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ICS 23.020.10

© 2006 CEN

EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG

Management Centre: rue de Stassart, 36

All rights of exploitation in any form and by any means reserved
worldwide for CEN national Members.

B-1050 Brussels

Ref. No. EN 14620-3:2006: E


EN 14620-3:2006 (E)

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Page

Foreword ............................................................................................................................................................. 4

Scope...................................................................................................................................................... 5

2

Normative references ........................................................................................................................... 5

3

Terms and definitions........................................................................................................................... 5

4

General ................................................................................................................................................... 5

5

Vapour tightness................................................................................................................................... 6

6
6.1
6.2
6.3

Materials................................................................................................................................................. 6
General ................................................................................................................................................... 6
Concrete................................................................................................................................................. 6
Pre-stressing and reinforcing steel..................................................................................................... 6

7
7.1
7.2

Design .................................................................................................................................................... 7
General ................................................................................................................................................... 7
Partial factors for actions and combinations of actions................................................................... 7

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1

Table 1 — Partial load factors for accidental actions .................................................................................... 7
7.3
Liquid tightness .................................................................................................................................... 7
8
8.1
8.2

8.3
8.4
8.5
8.6
8.7
8.8
8.9

Detailing provisions.............................................................................................................................. 8
General ................................................................................................................................................... 8
Pre-stressing ......................................................................................................................................... 8
Wall design ............................................................................................................................................ 8
Steel roof liner ....................................................................................................................................... 8
Construction joints ............................................................................................................................... 8
Position of tendons and wires............................................................................................................. 8
Concrete cover ...................................................................................................................................... 9
Minimum reinforcement ....................................................................................................................... 9
Reinforced concrete bund walls.......................................................................................................... 9

9
9.1
9.2
9.3
9.4
9.5
9.6

Construction and workmanship .......................................................................................................... 9
General ................................................................................................................................................... 9
Crack control ......................................................................................................................................... 9

Formwork and tie-rods ......................................................................................................................... 9
Spacers ................................................................................................................................................ 10
Curing................................................................................................................................................... 10
Tolerances ........................................................................................................................................... 10

10
10.1
10.2
10.3
10.4

Liners and coatings ............................................................................................................................ 10
General ................................................................................................................................................. 10
Liners.................................................................................................................................................... 10
Coatings ............................................................................................................................................... 10
Thermal Protection System (TPS) ..................................................................................................... 11

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Contents

Annex A (informative) Materials .................................................................................................................... 12
Figure A.1 — Notch on reinforcement bar..................................................................................................... 14
Annex B (informative) Pre-stressed concrete tank ..................................................................................... 15
Table B.1 — Summary of the advantages and disadvantages of joints in the wall to base
junction ...................................................................................................................................... 16

2


EN 14620-3:2006 (E)

Figure B.1 — Typical joints for pre-stressed wall and base junction......................................................... 17
Figure B.1 — Typical joints for pre-stressed wall and base junction (concluded) ................................... 18

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Bibliography ..................................................................................................................................................... 21

3


EN 14620-3:2006 (E)

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This European Standard (EN 14620-3:2006) has been prepared by Technical Committee
CEN/TC 265 “Site built metallic tanks for the storage of liquids”, the secretariat of which is held by
BSI.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by March 2007, and conflicting national standards shall
be withdrawn at the latest by March 2007.

EN 14620 Design and manufacture of site built, vertical, cylindrical, flat-bottomed steel tanks for the
storage of refrigerated, liquefied gases with operating temperatures between 0 °C and -165 °C
consists of the following parts:






Part 1: General;

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

Part 2: Metallic components;

Part 3: Concrete components;

Part 4: Insulation components;

Part 5: Testing, drying, purging and cool down.

According to the CEN/CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Cyprus, Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy,
Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia,
Slovenia, Spain, Sweden, Switzerland and United Kingdom.

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Foreword

4


EN 14620-3:2006 (E)

Scope

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This European Standard specifies general requirements for materials, design and construction of the
concrete components of the refrigerated liquefied gas storage tanks.
This European Standard deals with the design and manufacture of site built, vertical, cylindrical, flatbottomed steel tanks for the storage of refrigerated, liquefied gases with operating temperatures

between 0 °C and –165 °C.

2

Normative references

The following referenced documents are indispensable for the application of this European Standard.
For dated references, only the edition cited applies. For undated references, the latest edition of the
referenced document (including any amendments) applies.

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EN 206-1, Concrete — Part 1: Specification, performance, production and conformity

EN 1992-1-1:2004, Eurocode 2: Design of concrete structures — Part 1-1: General rules and rules for
buildings
EN 1992-1-2:2004, Eurocode 2: Design of concrete structures — Part 1-2: General rules — Structural
fire design
EN 14620-1:2006, Design and manufacture of site built, vertical, cylindrical, flat-bottomed steel tanks
for the storage of refrigerated, liquefied gases with operating temperatures between 0 °C and −165°C
— Part 1: General
EN 14620-2, Design and manufacture of site built, vertical, cylindrical, flat-bottomed steel tanks for the
storage of refrigerated, liquefied gases with operating temperatures between 0 °C and –165 °C —
Part 2: Metallic components

3

Terms and definitions

For the purposes of this European Standard, the terms and definitions given in EN 14620-1:2006 and
the following apply.
3.1
low temperature
temperature lower than –20 °C

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1

4

General

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For material selection and design of normal reinforced concrete and/or pre-stressed concrete
structures, reference is made to EN 1992-1-1.

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EN 14620-3:2006 (E)

5

Vapour tightness

Materials

6.1

General

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6

Material properties of concrete and components change at low temperature. Some changes are
beneficial, some non-beneficial. The appropriate material properties shall be used to ensure that the
structural integrity is not impaired for all temperature ranges for the components. This shall include
both steady state and transient conditions.
NOTE
Low temperature resistant material requirements, as given in 6.2 to 6.3, are needed only as far as
they are required to guarantee the structural integrity and to fulfil the liquid tightness and where applicable vapour
tightness requirements.

Concrete

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6.2

For normal and low temperature conditions, the concrete material requirements shall be in

accordance with EN 1992-1-1.
For the concrete performance, production, placing and compliance criteria, reference shall be made to
EN 206-1.
NOTE
Annex A.

6.3

6.3.1

Further information about the low temperature performance of concrete components is given in

Pre-stressing and reinforcing steel
Pre-stressing steel and anchors

Pre-stressing steel, anchors, ducts etc. shall be in accordance with EN 1992-1-1.

In addition, it shall be demonstrated that the pre-stressing steel and anchors are suitable for the cold
temperatures to which it may be exposed.
NOTE
Annex A.

Further information about the low temperature performance of pre-stressing concrete is given in

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To ensure vapour tightness of the outer tank (e.g. in a full containment tank) metallic liners or
polymeric coatings shall be used.

6.3.2

Reinforcing steel

For the design of reinforced concrete structure where the design temperature during a normal
operating or emergency condition does not fall below −20 °C, the reinforcing steel shall comply with
EN 1992-1-1.

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For elements under tension, where the design temperature during a normal operating or emergency
condition falls below –20 °C, additional low temperature requirements shall be implemented.

NOTE

Guidance is given in Annex A.

It shall also be demonstrated that reinforcement connectors, used at ambient temperature, are
suitable for the intended application.

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EN 14620-3:2006 (E)

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7

Design

7.1

General

Actions to be considered shall be in accordance with EN 14620-1:2006.

The reliability of the concrete components, according to the limit state theory, shall be achieved by
application of the partial factor method.

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The design values of actions, the effects of actions, material properties, geometric data and the
design resistance shall be determined in accordance with EN 1992-1-1. In case heat radiation is
involved, reference shall be made to EN 1992-1-2.

7.2

Partial factors for actions and combinations of actions

Table 1 provides partial load factors for accidental actions. They shall be used in addition to the partial
load factors mentioned in the EN 1991-1-1.
Table 1 — Partial load factors for accidental actions

Load combinations

Load factors

Dead

Normal action plus one
accidental action

Imposed

Adverse

Beneficial

Adverse

Beneficial

1,05

1,0

1,05

0

Abnormal
load

Wind

1,0

0,3

Accidental actions being, earthquake (SSE), blast overpressure, external impact, fire or leakage from inner
tank.

7.3

Liquid tightness

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For low temperature, the connectors shall be subjected to the same tests at design metal temperature
and the results of these tests shall be compared to those at ambient temperature. The connectors
shall be considered suitable if the low temperature results are within 5 % of those specified at ambient
temperature. The contractor shall carry out appropriate tests, which shall include, as a minimum, tests
for tensile strength and ductility. The results of these tests shall meet appropriate criteria set by the
designer.

For liquid tightness, the following shall be considered:
a)

In case of a non-liquid tight liner/coating

For concrete outer containers without a liquid tight liner or coating, the liquid tightness of the concrete shall be
ensured by means of the minimum compression zone of 100 mm.

In case of a liquid tight liner/coating

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b)

Where a liquid tight liner/coating is applied (to ensure full tightness of the secondary container) then
cracking of the concrete section shall be permitted within the limits specified by EN 1992-1-1.
In such cases the crack width shall be calculated and the liner/coating shall be proven to be capable
of ‘bridging’ a gap equal to 120 % of the crack width.

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EN 14620-3:2006 (E)

8

Detailing provisions

8.1

General

Pre-stressing

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8.2

For the pre-stressed concrete wall, horizontal pre-stressing shall be applied.

NOTE
Vertical pre-stressing is not required. It can be combined with horizontal pre-stressing. The need for
vertical pre-stressing depends on the tank design pressure, tank diameter, and associated permanent and
transitional stresses within the concrete section.

8.3

Wall design

The minimum wall thickness shall be determined so that:


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

adequate cover to all reinforcement and pre-stressing tendons shall be available;

8.4

space between the reinforcement and pre-stressing tendons shall be sufficient to ensure that a
homogeneous, liquid tight concrete structure is obtained.

Steel roof liner

The steel roof liner shall be anchored adequately to the concrete roof.

NOTE
The liner may act as formwork for the concrete and may also act compositely with the use of shear
studs. The concrete may be built up in layers to prevent overstress of the liner (see also B.6)

8.5

Construction joints

Attention shall be paid to the design and execution of the construction joints. The location and
necessity shall be carefully planned to minimize the risk of poor jointing. For the areas where liquid
tightness is to be assured, the contractor shall provide method statements based on proven working
practices and where necessary, due to lack of evidence, the contractor shall carry out tests to
demonstrate that the construction joint is liquid tight.

8.6

Position of tendons and wires

For internal pre-stressing systems using buttresses and grouted tendons, due account of the
emergency conditions, e.g. fire scenarios, shall be taken to determine the position of the pre-stressing
system.

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For general information on pre-stressed concrete tanks, reference should be made to Annex B.

NOTE 1
Tendons should be preferably placed, in the centre of the concrete wall for protection against
external fires.

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The tendons shall be well protected from corrosion during the life of the tank. Grouting procedures
shall be provided and agreed between the designer and contractor to provide adequate protection to
the tendons.
NOTE 2
In very aggressive environments, where additional protection is required, for the tendons, non-ferrous
pre-stressing ducts may be considered. Reference is made to ‘Durable bonded post-tensioned bridges’ Concrete
Society Report TR47 [12]. For non-bonded tendons, reference should be made to FIP recommendation 91 [13].

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EN 14620-3:2006 (E)

NOTE 3
Where wire-winding systems are used the wire should be placed on the outer face of the wall in a
continuous helix with vertical spacing between wires of not less than 8 mm. Each layer of wire should be coated
with shotcrete to provide a minimum of 6 mm thickness over the wire. After all the wires have been placed and
coated, a final coating of shotcrete should be applied to provide a minimum thickness of 25 mm over the last
wire.

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Concrete cover

The concrete cover selection of reinforcement shall take into account the exposure classification, soil
conditions and emergency design conditions e.g. fire protection.
Minimum requirements shall be in accordance with EN 1992-1-1.

8.8

Minimum reinforcement

The minimum area of reinforcement shall be in accordance with EN 1992-1-1.

8.9

Reinforced concrete bund walls

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Bund walls constructed in reinforced concrete shall be permitted. The bund wall shall be designed to
the requirements specified in this European Standard.

NOTE
Bund walls are required with a single containment tank. They can be applied in combination with an
earth embankment for structural reasons.

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9.1

Construction and workmanship
General

In principle, the construction and workmanship requirements shall be in accordance with EN 1992-11.
Special attention shall be paid to the concrete composition, production, quality control, placement,
compaction, curing etc. of the concrete to ensure liquid tightness of the structure, which shall be in
accordance with EN 206-1.
In addition, the following requirements shall apply.

9.2

Crack control

The contractor shall investigate the heat of hydration and the effects of drying and thermal shrinkage
in the concrete structure. The composition of the mix, the cement type, and the intended execution
method shall be adapted accordingly so that cracking of the concrete is minimized.

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8.7

Temperature differences between new and old constructions and the environment shall be considered
in the construction plan.

Formwork and tie-rods

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9.3

The formwork shall be tightly sealed at all joints. Calculations of the formwork shall be made to ensure
sufficient strength and stiffness.
Special arrangements shall be applied at tie-rods to prevent leakage.
All cone openings shall be sealed such that liquid tightness shall be ensured.

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EN 14620-3:2006 (E)

9.4

Spacers

Spacers shall be used to provide correct cover to the reinforcement and they shall be product
resistant and liquid tight.

Curing shall be performed in accordance with EN 206-1.
NOTE
mix.

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Curing

Curing is dependent on many factors including wind speed and temperatures of the air and concrete

The curing period shall include measures to prevent excessive evaporation and to stabilize the
temperature effects caused by heat of hydration until the concrete matrix gains sufficient internal
strength to withstand both internal and external stresses incurred.

9.6

Tolerances

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General tolerance requirements of the concrete structure shall be in accordance with EN 1992-1-1.
The contractor shall investigate the necessity for stricter tolerances e.g. special linings and for certain
insulation systems (membrane tanks).

10 Liners and coatings
10.1 General

Liners and coatings shall be applied on the concrete internal surface in order to avoid moisture and
vapour penetration through the structure.
NOTE

Liners and coatings may also be used to ensure liquid tightness of the structure.

The following materials shall be used:



steel plates as liners;

reinforced or un-reinforced polymeric layers as coatings.

10.2 Liners

Steel liners shall be considered vapour and liquid tight as long as the material selection is appropriate.
The material selection shall be based on the design metal temperature to be determined by the
contractor. Steel type selection shall be made in accordance with EN 14620-2.

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9.5

The minimum thickness of the plate shall be 3 mm.
Any creep or long-term deformation of the concrete due to operational conditions applied to the
structure shall be taken into account for the design of the liner.

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The anchoring system shall be designed for combined shear and tension.

10.3 Coatings
Liners or coatings shall be applied as vapour barrier or as vapour/liquid barrier. The coatings shall be
applied directly to the concrete surface. Prior to application, the concrete surfaces shall be grit blasted

10

EN 14620-3:2006 (E)

and subsequently vacuum cleaned. All remains of release agents and curing compounds shall be
removed if these are not compatible with the coating system.
When the coating functions as a vapour barrier, the following shall apply:
2

maximum water vapour permeability shall be 0,5 g/m 24 h.



coating shall not degrade after long-term contact with the product (vapour).
NOTE 2



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

The recommended test method is ASTM D1647 or equivalent.

bond strength of the coating to concrete shall exceed 1,0 MPa.
NOTE 4



The recommended test method is immersion in product vapour for at least three months.

coating shall not deteriorate under the influence of the concrete. The coating shall be alkali
resistant.
NOTE 3



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NOTE 1
The recommended test method is ASTM E96 under temperature/humidity conditions equal
to the climatic conditions of the location of the project.

The recommended test method is EN ISO 4624 or equivalent.

escape of vapour shall be limited. This shall be considered acceptable when the permeability of
2
product vapour is restricted to 0,1 g/m 24 h;
coating shall have sufficient flexibility to be capable of bridging crack widths. A bridging capability
value of 120 % of the calculated design crack width at normal operating temperatures shall be
used.
NOTE 5

The test method should be proposed by the contractor.

Where the coating also acts as a liquid barrier, additional tests shall be performed. The contractor
shall demonstrate that the coating does not degrade after short time (splashing) and long time
(three months) liquid exposure.

10.4 Thermal Protection System (TPS)

When a TPS is applied, the following subjects shall be considered:


all possible actions, including hydrostatic pressure of the product, vapour pressure, effects of
creep and shrinkage of the concrete and steel plate;

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



adequate liquid tightness of the wall section at the top (concrete cracking);



sufficient height of the wall section.

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The height of the wall section shall be at least 500 mm above any temporary construction opening.

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EN 14620-3:2006 (E)

Annex A
(informative)

For concrete, the following general information is provided:

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A.1 Concrete

for pre-stressed concrete the class of concrete should be at least fck 40 of EN 1992-1-1:2004;



enhanced strength, that is known to exist for concrete as a material of construction at low
temperature, is normally not used in determining the ultimate strength of concrete sections.
However, when adequate testing data is available, the low temperature properties may be
utilized;










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

reduced expansion coefficient, thermal properties and Young’s modulus should be considered for
design verification;
strength increase caused by high strain rates (e.g. valve impact) should be considered when
appropriate;
use of high strength concrete and/or fiber admixtures may be considered appropriate for certain
applications;
use of a low water/cement ratio is essential. It reduces the pore water within the concrete matrix.
The freezing of pore water causes an expansion of about 9 %. Some of this expansion is taken
up within existing air voids but, if there is excessive water, internal cracking of the concrete can
result;
concrete mix may contain up to 5 % entrained air. Air entraining agents should be resin based in
accordance with the relevant standard. Metallic based agents should not be used;
it should be ensured that no adverse effects from using combinations of concrete additives can
take place;
ground granulated blast furnace slag or pulverised fuel ash may be used in combination with
Portland cement. These materials assists in reducing the heat of hydration of thick concrete
sections and thus reducing the early thermal shrinkage;

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Materials

whilst the introduction of cement replacement materials may be beneficial in terms of the

reduction of early shrinkage and enhanced resistance to environmental pollution, users should be
aware that there may be a slower strength gain;



prolonged contact with hydrocarbon products has no significant detrimental effect on the
properties or useful life of concrete, even at ambient temperatures;

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



12

microsilica may be considered to improve the resistance to corrosion.


EN 14620-3:2006 (E)

A.2 Pre-stressing steel and anchors

greatest load to the concrete structure occurs during construction, when the tensile load is
applied to the pre-stressing steel tendons or bars. The jacking stress in the steel tendon is around
80 % of the yield strength of the tendons. Thereafter the applied stress to the steel tendons
reduces due to lock-off, transfer, relaxation and creep. This forms part of the reason why
hydrostatic testing is not required for the secondary container of double and full containment
tanks;



pre-stress losses and numerical values are ascertained for the steel at ambient temperature as a
conservative assessment as the steel characteristics improve at low temperature;



if the design temperature is lower than 50 °C, then it should be demonstrated by testing that the
pre-stressing system (bars, strands and anchors) is suitable for the cold temperatures to which it
may be exposed. In this respect the following literature should be considered:

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

"cryogenic behaviour of materials for pre-stressed concrete" [14];

2)

"Assessment of mechanical properties of structural materials for cryogenic applications" [15].

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1)

A.3 Reinforcing steel
A.3.1 Sampling

For the testing of the bars, fully finished bar should be sampled from two production heats, from the
maximum and minimum bar diameter for the order, and from all strength grades to be used. The
minimum rate of specimen testing should be in accordance with EN 10002-1. Testing should be carried
out in accordance with EN 10080 where test records are not available from the manufacturer.

A.3.2 Testing

Tensile tests should be carried out under cold condition (at the design metal temperature) to establish
the suitability of the steel.
NOTE
The design metal temperature should be the lowest temperature that the reinforcement bar would be
subjected to under abnormal loading conditions.

During the test, the specimen temperature should be as uniform as possible. The difference between
the temperature at any two points of the specimen or the difference between the temperature at any
point and the design temperature should not exceed 5 °C.

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For the design of pre-stressed concrete structures the following information is provided:

Tensile tests in accordance with EN 10002-1 should be conducted on un-notched and notched bar
specimens.
The following criteria should apply:

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1) The Notch Sensitivity Ratio (NSR) should be:

NSR =

Tensile strength of notched bar
0,2% proof stress of unnotched bar

or:

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EN 14620-3:2006 (E)

NSR =

Tensile strength of notched bar
Lower yield stress of unnotched bar

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The test specimen for notched bar tests should be notched at the half-length position between the
machine grips. A V-notch should be used that has an internal angle of 45° and a radius at the base of
0,25 mm. Machining techniques and tolerances should be in accordance with EN 10045-1. For
longitudinal ribbed bars, the notch should be placed across the rib and penetrate 1 mm into the
underlying bar. For transverse ribbed bars, the notch should be placed on the crown (see Figure A.1).

1

1 mm

a) longitudinal ribbed bar

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1

1 mm

b) transverse ribbed bar
Key
1

V-notch

Figure A.1 — Notch on reinforcement bar

2) Plastic elongation

Each un-notched specimen should demonstrate a percentage plastic elongation of at least 3 %. The
percentage plastic elongation is the permanent percentile increase of the original gauge
length corresponding to tensile strength.
3) Yield strength

In addition, the yield strength of the un-notched specimen found during testing should be at least
1,15 times the minimum yield strength used in the design.

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A NSR value of 1 or greater is required to achieve acceptable toughness.

A.3.3 Alternative solutions
The following alternatives may be considered:

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



use of carbon-manganese steel, 9 % nickel steel or austenitic stainless steel. Various grades of
stainless steel reinforcement are available complying with EN 10088-1. The ductility of most
austenitic stainless steels is maintained down to –196 °C;
reinforcing or pre-stressing steel with reduced allowable tensile stress.

NOTE
ANSI/NFPA 59A recommends a maximum allowable tensile stress for reinforcement for tanks for
LNG. This is significantly lower than the stress permitted for ambient temperature, and may result in an
uneconomic design, but can be justified where special steel is not available or economically unacceptable.

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EN 14620-3:2006 (E)

Annex B
(informative)

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B.1 General

The following publications give reference information on details and parameters for the design of
prestressed concrete tanks:
Turner F.H. Concrete and cryogenics [16];



Bruggeling, A.S.G. Prestressed concrete for the storage of liquefied gases [17];



Preliminary recommendations for the design of prestressed concrete containment for the storage
of refrigerated liquefied gases [18].

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

Pre-stressed concrete is most suitable for liquid tight concrete structures. Therefore, it is used for the
wall of the tank. The bottom and the roof are often made of normal reinforced concrete.

B.2 Pre-stressing system

Horizontal pre-stressing is always required. The need for vertical pre-stressing depends on the design
of the tank (design pressure, thickness of roof etc.).
Horizontal pre-stressing could be provided by means of the following techniques:



horizontal tendons positioned in ducts within the concrete wall of the tank, extending between the
buttresses formed on the outer face of the tank wall;
an aggregation of tendons formed by winding wire or strand around the outer face of the wall.

NOTE

Wire winding systems should be placed on the outer face of the wall in a continuous helix with
vertical spacing between wires of not less than 8 mm. Each layer of wire should be coated with shotcrete to
provide a minimum of 6 mm thickness over the wire. After all wires have been placed and coated as described, a
final coating of shotcrete should be applied to provide a minimum thickness of 25 mm over the last layer of wire
(AWWA D110).

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Pre-stressed concrete tank

B.3 Base slab

The tank base slab could be made of either pre-stressed or reinforced concrete.

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In the case of pre-stressed concrete where piles are used, movement of the slab from pre-stress
forces shall be considered in the design.
NOTE
Often the base slab is made in sections with construction joints. Full attention should be paid to the
execution of the construction joints so that a monolithic structure is ensured.

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EN 14620-3:2006 (E)

B.4 Wall to base junction

fixed joint: in such a case the concrete structure is monolithic. The movement of the wall, relative
to the base slab, is prevented. The joint is designed to accept the relatively large moments and
shears which arise as a consequence;



sliding joint: the wall is supported by the base slab and may move horizontally. The wall is free to
move horizontally. It is supported by the base slab. Generally it is necessary to ensure that the
outer tank cannot move laterally. Radial guides should be provided to ensure that the movement
is concentric with the base slab. A flexible seal, commonly in the form of a stainless steel strip,
should be provided to prevent leakage of liquid or gas;



pinned joint: the wall is also supported by the base slab, it is fixed horizontally, (usually after post

tensioning) and has the capability of limited rotation. Substantial shear is transferred from wall to
base slab, but the joint is not required to transmit bending moments. The custom is to allow the
wall to slide while it is being pre-stressed. Thereafter it is pinned in position, by one of several
devices, but not prevented from vertical rotation.

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

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A summary of the advantages and disadvantages of each type of joint is given in Table B.1.

Table B.1 — Summary of the advantages and disadvantages of joints in the wall to base
junction

System

Advantages

Disadvantages

Sliding joint

Stresses are predicted with good
reliability

Dependent on adequacy of joint seal

Secondary stresses are relatively small

Some uncertainty over degree of sliding
obtained

Pre-stress is predicted with good
reliability

Subsequent secondary stresses are
less reliable

Maximum moment occurs in wall away
from the joints, at level where "end
effects" from vertical tendons are largely
smoothed out

Large shears and fairly large moments

Robust form of construction

Larger moments and shears

Pinned joint

Fixed joint

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The wall to base connection could be designed as a:

Full vertical pre-stressing in bottom of
wall

Maximum moment occurs at the joint

The fixed joint concept is preferred for liquid tightness.

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For LPG tanks, the fixed joint can be designed for the low temperature to which it may be exposed in
case of a primary container leakage. This is not the case for LNG tanks. The wall to base connection
has to be protected by TPS.
The three different designs of joint are shown in Figure B.1.

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EN 14620-3:2006 (E)

6

12

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7
8

3

9

2
1

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a) Sliding joint

6

4

7

8

10

3

2

11

1

b) Pinned joint

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5

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Figure B.1 — Typical joints for pre-stressed wall and base junction

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EN 14620-3:2006 (E)

6

4

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7

2

10

1

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c) Fixed joint
Key
1
2
3
4
5
6

tank base

7

pre-stressed wall

base reinforcement

8

stainless/nickel steel seal

bearing plate

9

radial strap

circumferential pre-stress

10

pre-stressing anchorage

wall reinforcement

11

grout

vertical pre-stress

12

wire wound circumferential pre-stress with
shotcrete layer

Figure B.1 — Typical joints for pre-stressed wall and base junction (concluded)

B.5 Wall to roof junction

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The wall to roof connection is usually made of a monolithic construction.

B.6 Roof

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The use of a concrete roof is usually advantageous in case a high design pressure (design pressure
> 140 mbar for example) is applied.
The roof is normally made of reinforced concrete. An internal steel liner is used to ensure the vapour
tightness of roof. This liner can be used as formwork and may act as a composite structure. In this
case, the liner is anchored to the concrete by studs.

18